UNITED NATIONS - A UN Security Council committee on Thursday imposed sanctions on two Iranian firms that violated a UN arms embargo on Tehran by shipping weapons to the Syrian government.

The move was welcomed by the United States. US Ambassador to the United Nations Susan Rice said in a statement that the two firms blacklisted by the Iran sanctions committee were "significantly involved in Iranian arms smuggling, including smuggling to Syria."

"These companies - Yas Air and SAD Import Export Company - were responsible for shipping ammunition, assault rifles, machine guns, mortar shells and other arms from Iran to Syria," she said.

"The committee's decision underscores the growing international concern over Iran's use of the transportation and shipping sectors as a means to export arms and conduct other illicit activities in violation of UN sanctions," Rice said.

A UN panel of experts that monitors compliance with the Iran sanctions regime had recommended earlier this year that the sanctions committee add cargo airline Yas Air, SAD Import Export Company, and one other firm to the UN blacklist.

The Security Council has imposed four rounds of sanctions on Iran for refusing to halt its nuclear enrichment program, which the United States, European Union and their allies suspect is at the heart of a weapons program. Iran rejects the allegation and refuses to halt what it says is a peaceful energy program.

Among the punitive measures Iran was hit with was a ban on arms exports.

The Security Council has not banned arms sales to Syria, which means countries like Russia can theoretically continue supplying the government there with weapons as it struggles to suppress a 21-month-long uprising by rebels seeking to oust Syrian President Bashar Assad.